In case where an air bag is provided for protecting an occupant sitting on a vehicle seat, an occupant judging device for a vehicle seat has been provided at the vehicle seat for determining whether an occupant is seated or not on the corresponding seat, the occupant is an adult or a child, or the like. Japanese Patent Laid-open Publication No. H09-207638 discloses a known occupant judging device. The disclosed device includes a plurality of weight sensors provided at a plurality of fixing positions respectively of a seat body with respect to a vehicle floor, and a controller for calculating a detection weight value based on weight values outputted from the plurality of weight sensor and for determining whether an occupant is seated on the vehicle seat or not based on the calculated detection weight value. More specifically, the controller calculates a detection weight value by summing up the detection values outputted from the plurality of weight sensors respectively by an adder, compares this detection weight value with a weight value set in advance (threshold value for determination), and determines whether an occupant is seated on the vehicle seat or not by comparing the detection weight value and the threshold for judgment.
The vehicle seat on a passenger side may be equipped with a CRS (Child Restraint System). Thus, when the occupant judging is preformed, a state whether the CRS is equipped or not is included in judgment to prevent a case in which a child sitting on the CRS installed on the seat is misjudged as an adult.
The CRS is generally equipped on the seat body with a seatbelt. It has been confirmed that when the CRS is installed on the seat, a large load is added to the seat by tightening with the seatbelt, and is decreased after the CRS is tightened with the seatbelt. Thus, it is proposed that the detection weight value after the seatbelt is fastened is monitored and a CRS judgment (judging whether the CRS is installed or not) is performed by detecting an action of installing the CRS.
However, if an adult sitting on the seat leans against a door and thus his/her hip is lifted up, the detection weight value may be decreased. This situation can be misjudged as the CRS installation according to the detection weight decrease.
Thus, a need exists for an occupant judging device for a vehicle seat which can prevent a child restraint system from being misjudged as installed.